The present invention relates to comminuting apparatus for rock, concrete or the like, and more particularly to improvements in impact crushers of the type wherein a rotor provided with beater bars or the like entrains and propels material to be comminuted against one or more adjustable impact or grinding means.
It is already known to mount the impact or grinding means, hereafter called "impact means" for simplicity, for movement about a pivot axis which is parallel to the rotor axis and to bias the impact means toward the periphery of the rotor by one or more springs which assist the action of gravity and tend to reduce the width of the gap between the impact means and the path of movement of beater bars, or analogous comminuting elements at the periphery of the rotor. It is also known to couple the impact means to one or more elongated members (e.g., feed screws) which extend from the housing of the impact crusher and are connected to each other by a crosshead. The extent to which the impact means can pivot toward the periphery of the rotor is determined by one or more stops which are mounted at the outer side of the housing and are located in the path of movement of the crosshead. The crosshead can be moved relative to the housing by a suitable motor, e.g., a hydraulic cylinder and piston unit which is disposed between the housing and the crosshead. The connection between the cylinder and piston unit and crosshead and/or housing is designed to have a lost motion to enable the impact means to yield freely away from the rotor.
The extent to which the crusher can comminute material which is being fed into the housing to pass between the rotor and the breaker depends primarily on the width of the gap between the beating, elements at the periphery of the rotor and the nearest portion of the impact means. The adjustability (pivotability) of the impact means is intended to enable an operator to change the extent of comminuting action as well as to compensate for pronounced wear on those portions of the rotor and impact means which come into contact with the material to be comminuted. The mounting of the impact means in a selected angular position should not be rigid because the impact means must be capable of yielding (i.e., of increasing the width of the gap) if such gap receives one or more non breakable objects which are sufficiently large to necessitate a temporary widening of the gap. As mentioned above, the impact means normally tends to pivot nearer to the rotor, either by gravity alone or by gravity as well as under the action of one or more resilient elements in the form of helical springs or the like.
In certain types of presently known impact crushers, the width of the gap between the impact means and the circle swept by the beating elements of the rotor is changed by changing the positions of feed screws relative to the crosshead. This involves rotation of nuts which mesh with the feed screws at both sides of the crosshead. In view of the fact that many impact crushers are very large and are designed to comminute extremely hard substances, the dimensions of feed screws and nuts are also substantial which means that rotation of nuts relative to the feed screws necessitates the exertion of very pronounced effort. Moreover, the nuts are likely to jam because of the hard shocks they have to take up or to stick due to accumulations of dust in the threads of feed screws. Therefore, such nuts cannot always be manipulated by hand which contributes to the cost of the operation. Moreover, each and every adjustment necessitates a stoppage of the crusher because the likelihood of injury to attendants is much too great if the nuts are to be rotated while the beaters of the rotor propels solid particles against the impact means.
The manner in which the aforementioned cylinder and piston unit can be used to prevent or eliminate bridging of material in the interior of the housing of an impact crusher is disclosed in "Prinzip und Moeglichkeiten der Prallzerkleinerung" aus "Zement-Kalk-Gips" (Year 18, 1965, Vol. 11 pages 580-588). There is described the possibility of increasing the width of the gap between the rotor and the impact means; however, the publication does not offer any suggestion to locate and retain the impact means in any one of several selected positions. The main purpose of the construction which is disclosed in that publication is to relieve the nuts on the feed screws in order to facilitate manual rotation of the nuts. Such operation is time-consuming because the sequence in which the loosening of nuts and lifting of the crosshead take place changes in dependency on the desired direction of adjustment. Moreover, a person must climb onto the housing of the crusher in order to loosen the nuts. Purely hydraulic adjusting systems are too complex and the interval required for an adjustment is too long. Reference may be had to German Offenlegungsschrift No. 2,037,104.